Mniaceae. Genus Rhizomnium

1. Upper leaf apices broadly acute; capsules striate when dry; plants small; restricted to southern parts of the Russian Far East 1. R. parvulum

This species has the smallest plants in the genus; it differs from all other Russian species of Rhizomnium by the presence of broadly acute (not rounded) leaves and dwarf males.

— Upper leaf apices rounded; capsules smooth when dry; moderately small to robust plants; wide spread in Russia 2

2. Upper leaves ovate-oblong to oblong-spatulate 4. R. striatulum

An East Asian species known in Russia from Kamchatka, Sakhalin, Kuril Islands and Primorsky Territory. It is a montane, forest zone species that grows on moist rocks, wet cliff ledges, moist soil and rotten wood. It can be recognized by the following combination of features: comparatively small plants; obovate-oblong to oblong-spatulate upper leaves; and small, elongate leaf cells.

— Upper leaves suborbicular, obovate or obovate-spatulate 3

3. Micronemata and their initial cells absent; plants dioicous 4

— Micronemata and their initial cells present; plants autoicous or synoicous 7

4. Leaves 1.8–2.4 mm long, not apiculate 6. R. andrewsianum

This arctomontane species is known from a few collections in northern European Russia and is sporadically distributed in the northern and mountain areas of Asian Russia (Polar Urals, Taimyr, Yakutia, Chukotka, Altai Mts., Kamchatka and Commander Islands). It is found at all altitudinal zones in the mountains and often in boggy places in the Arctic tundra. Rhizomnium andrewsianum can be recognized by its small plant size; reddish color; dark stems without micronemata; almost circular leaves that lack apiculi; and unistratose marginal leaf borders.

— Leaves 3–6 mm long, apiculate or not 5

5. Leaves suborbicular, not apiculate; marginal leaf border unistratose 5. R. nudum

This East Asian and western North American species is found in the Russian Far East (Kam­chatka, Commander and Kuril Islands, Khabarovsk Territory near the sea shore) and south Irkutsk Province (near Lake Baikal). It is a montane forest and tundra species that grows on wet soil among tall grasses, stream banks, and decaying wood. It can be recognized by its dioicous sexual condition; dark-colored stems without micronemata; large, elliptic to almost round leaves that lack apiculus; and mostly unistratose marginal leaf borders.

— Leaves obovate, apiculate; marginal leaf border multistratose 6

6. Rhizoids with multicellular gemmae; leaves nar­rowly triangular at base (leaf margins forming ca. 25–30° angle with costae) 3. R. tuomikoskii

Previously considered endemic to Japan, R. tuomikoskii is now known in the Russian Far East from Kamchatka, Sakhalin, Southern Kuril Islands, and the Primorsky Territory. It is a montane forest species (to 800 m) that grows on wet, stream bank soil and decaying wood. It is similar to R. punctatum in having a dioicous sexual condition; no micronemata; bistratose marginal leaf borders; and small leaf apiculi. It differs from R. punctatum in having narrower leaf bases; better developed rhizoidal macronemata that often extend to the upper rosette of leaves; and frequent multicellular, rhizoidal gemmae.

— Rhizoids without multicellular gemmae; leaves broadly triangular at base (leaf margins form ca. 35–40° angle with costae) 2.R. punctatum

Rhizomnium punctatum is widespread in European Russia (mainly in the forest zone) and rather frequent in the Altai Mts. Elsewhere in Asian Russia it occurs sporadically in Siberia (West Siberia and southern Taimyr). Although reported from the eastern part of Asian Russia, all records from this area are based on misidentifications. It grows on soil, litter and rotten wood in wet places (along streams, boggy forests, swamps, and near springs). Rhizomnium punctatum can be recognized by its dioicous sexual condition; lack of micronemata; multistratose marginal leaf borders; and small leaf apiculi. For its differences from R. tuomikoskii see comments under that species.

7(3). Plants synoicous 7. R. pseudopunctatum

This is one of the most common species of Rhizomnium in the northern boreal zone, Arctic and high mountain areas of Russia. It has a scattered distribution in other Russian regions. The species can be recognized by its robust plants; stems with dense micronemata; mostly unistratose leaf borders; and synoicous sexual condition.

­— Plants dioicous 8

8. Plants 3–6(–10) cm high; leaves obovate or widely elliptic, 4–9 mm long; median leaf cells 80–100(–130) mm long 8. R. magnifolium

In European Russia R. magnifolium is common in the northern areas, but rare in the central regions. It is also known from a few records in South Urals and the Caucasus, as well as sporadically distributed in Southern Siberia and the Russian Far East, but barely extends into permafrost areas. It is found mainly in montane forest zones growing on soil, rocks and rotten wood in forests and along streams. Rhizomnium magnifolium is characterized by its large, pale-green plants; dioicous sexual condition; stems with micronemata; ovate capsules; and yellow exostome teeth.

­— Plants 1–3(–5) cm high; leaves obovate or suborbicular, 1.5–4.5 mm long; median leaf cells 35–80(–100) mm long. 9. R. gracile

This mainly northern North American species is known also from Finland. In Russia it is sporadically distributed in the Northern Far East (Chukotka to Magadan Province, Kamchatka and the Commander Islands). It occurs from sea level to 1300 m and grows on wet soil in tundra, pools in bogs and along streams. It is similar to R. nudum and R. andrewsianum in having round leaves that lack apiculi and unistratose marginal leaf borders. It differs from R. nudum in having smaller leaves (1.5–3 vs. 4–6 mm long), and different colored plants (reddish vs. dark-green). Rhizomnium gracile differs from R. andrewsianum in having at least a few stem micronemata (no stem micronemata in R. andrewsianum).